1. Field of the Invention
This invention relates to an image holding member for holding electrostatic images or toner images, and more particularly, to an image holding member of excellent durability, cleaning property and the like containing graft polymers in the surface layer.
2. Description of the Related Art
Electrostatic images or toner images are formed by various electrophotographic processes. As an image holding member bearing the produced images, there are image holding members having a photoconductive layer, so-called "electrophotographic photosensitive member", and those having no photoconductive layers.
An electrophotographic photosensitive member may have various embodiments depending on the type of electrophotographic process. Representative electrophotographic photosensitive members are a photosensitive member constituted of a support and a photoconductive layer overlying the support and a photosensitive member having an image holding member constituted of a photoconductive layer and an insulating layer. These are widely used.
Electrophotographic photosensitive members are subjected to a predetermined electrophotographic process to form electrostatic images and visualize the electrostatic images by developing. The surface layer of the image holding member is subjected to various treatments, for example, electrical and mechanical treatments such as charging, exposure, development, transferring, cleaning and the like. Therefore, it is necessary for repeated use of a photosensitive member that the surface layer exhibits a high durability to such treatments. In particular, durability against surface damages is very important. On the other hand, remaining toner particles after transferring, paper powders of receiving papers, and decomposition products formed by ozone generated by corona charging are attached to the surface layer. There fore, when the cleaning treatment is insufficient, the remaining toner particles are fused and adhered to the surface layer and the surface resistance is lowered resulting in degradation of image quality. Therefore, for the purpose of satisfying the need for repeated durability, the surface layer of the image holding member is required to have a good cleaning property.
Heretofore, it has been attempted to add a material capable of imparting a lubricating property to the surface layer for satisfying the above-mentioned properties. Examples of the material are ordinary coating film surface modifying agents such as leveling agents, silicone oils and the like. As another method, Teflon powders may be dispersed. However, ordinary surface modifying agents have poor compatibility with components of a liquid coating material to be added so that the surface modifier is transferred to or exudes from the surface layer during use for a long period of time. As a result, the duration of effect of the surface modifier is problematic. In addition, when the surface layer itself forms a photoconductive layer, the surface modifying agent is not compatible with a photoconductive material and is liable to become a trap to movement of carriers generated by light. Therefore, there is a tendency that the residual charge increases during repeating electrophotographic processing. On the other hand, in case of a surface layer in which Teflon powders are dispersed, there are problems such as poor dispersability, lowered transparency, trapping carriers and the like.